Naturally occurring auxins, which are plant hormones which in minute quantities act to promote or modify plant growth as in root formation, are known. Such compositions include indole-3-acetic acid (hereinafter denoted IAA) which is known to stimulate adventitious root formation in cuttings of the easy-to-root plants, otherwise known as "good rooters" (Went et al. 1937, Phytohormones, Mac Millan Co., N.Y. page 294). Synthetically prepared auxins such as indole-3-butyric acid (IBA) and Naphthalene-acetic acid (NAA) have more effectively induced rooting in cuttings, particularly cuttings of difficult-to-root species, otherwise known as "poor rooters" (Audus, 1959, Plant Growth Substances, 2nd edition, Interscience Publications Inc., N.Y., page 553; also see Hartmann and Kester, 1975, Plant Propagation, 3rd edition, Prentice-Hall, Inc., Englewood Cliffs, N.J.)
Simple phenols, when administered in admixture with an auxin sometimes cause a synergistic response in adventitious root initiation (Haissig, 1974, Influences of auxins and auxin synergists on adventitious root primordium initiation and development, New Zealand Journal of Forestry Science 4(2); 311-323; also Gorter, Physio. Plant. 1962, 15: 88 to 95). Several theories have been proposed to explain the synergism, one theory being that auxin molecules become bonded to the phenolic moiety and that the conjugated composition induces root initiation more effectively than either the auxin or the phenolic compound individually.
Methyl or ethyl esters of auxins have sometimes been shown to enhance adventitious root initiation more effectively than the corresponding free acids (Veldstra, 1944, Researches on Plant Growth Substances, Enzymologia II, pp. 97-163). The naturally occurring auxin IAA at times appears naturally esterified to form other compounds, and poorly defined auxin phenolic conjugates have been reported (Schantz, 1966, Chemistry of naturally occurring growth regulating substances, Ann. Rev. Plant Physiology, 17:409-438).
A U.S. patent to Grace, U.S. Pat. No. 2,204,213 discloses the use of indole-3-acetic acid, indole-butyric acid, naphthyl acetic acid, phenyl-acetic acid, indole-propionic acid and the salts and esters thereof as auxins or plant hormones for stimulating seed germination and plant growth therefrom of wheat, barley, soya bean and tomato seeds.
Among the known auxins, IAA does not appear to work effectively as a rooting hormone on woody as opposed to herbaceous cuttings. All commercially available rooting hormone preparations comprise IBA, NAA, amides of naphthylene-acetic acid, mixtures of the foregoing, or mixtures of the foregoing with IAA. These synthetic auxin preparations have been available for many years but are generally unsatisfactory as plant hormone root initiators for "poor rooters" and "non-rooters", and prior to Ser. No. 052,656 no more effective preparations have appeared over the years despite the need for more effective plant rooting hormones (New Vistas in Plant Propagation, International Plant Propagators Society Combined Proceedings, 1977, 27:106-113).
It has been reported that phenyl indole-3-acetate (P-IAA) produced 2 to 4 times as many root primordia per leafy bean cutting (Top Crop), an herbaceous plant, (Influence of phenyl indole-3-acetate on adventitious root primordium initiation and development, Plant Physiology (Supplement) 61 (4):65).
A logical applied compound to enhance root primordium initiation (other than mixtures of auxins and phenolics, as described above) would appear to comprise a molecule resulting from a carboxylic acid-phenol esterification reaction, or an analogue or derivative thereof. Synthesis of such esters as phenyl indole-3-butyrate and 3-hydroxyphenyl indole-3-acetate has been attempted (Nekuda, 1976, Synthesis of derivatives of indole-3-acetic acid, M.S. Thesis, South Dakota School of Mines and Technology; Giacoletto, 1978, Synthesis of derivatives of indole-3-acetic acid, M.S. Thesis, South Dakota School of Mines and Technology). The Nekuda and Giacoletto MS theses are both incorporated herein by reference. Testing the aforementioned aryl esters on bean (Phaseolus vulgaris cv. Top Crop) cuttings provided that phenyl and 3-hydroxyphenyl indole-3-acetate are ten or more times as effective, on a molar basis, as compared with indole-3-acetic acid. These esters had no effect on jack pine (Pinus banksiana Lamb.) cuttings because only more active synthetic auxins, such as indole-3-butyric acid (IBA) and naphthalene acetic acid (NAA) usually induce primordium root initiation in woody plant cuttings to any substantial degree (Haissig, 1979, Influence of aryl esters of indole-3-acetic acid and indole-3-butyric acids on adventitious root primordium initiation and development, Physiologia Plantarum 47:29-33).
Phenyl indole-3-butyrate, however, yielded more rooted jack pine cuttings than did indole-3-butyric acid treatment. It was therefore concluded that certain aryl esters may be synthesized that are more effective in inducing adventitious root initiation than other phenyl or 3-hydroxyphenyl esters and than other aryl esters of non-indole auxins, such as naphthalene-acetic acid (Haissig et al. patent application Ser. No. 052,656, referred to above).
The development of new synthetic procedures for preparing new auxins or plant growth regulators is discussed in an article published in 1980; see Boyles M.S. thesis, South Dakota School Mines and Technology. This Boyles M.S. thesis is likewise incorporated herein by reference.